Field of the Invention
The present invention relates generally to the design of electrical circuits and specifically to a method of producing electrical circuits on the surfaces of three-dimensional objects.
Many electrical or electronic circuits are made by means of printed circuit boards (PCB's) in which electrical conduction paths are defined as traces of copper on the surfaces of a flat sheet of insulating material. In more complex versions, there may be multiple layers of circuit, for example, on the two sides of the PCB, which are connected to each other by plated through holes or vias in the PCB.
PCB's provide both electrical connection and mechanical support for electronic components such as resistors, capacitors and integrated circuits. In addition, PCB's may include connectors used to couple the circuit, for example, to power sources, transducers or to other circuits. Generally, PCB's are protected and supported in cases or other structures to make usable appliances.
In contradistinction to the flat two-sided nature of the conventional PCB, a molded circuit board (MCB) is generally a three-dimensional object, having multiple surfaces. Thus, an MCB may combine both mechanical features and electrical functions into one artifact.
This combined functionality is not achieved without some cost, since the design of such an MCB combines the mechanical design technology of molded or solid parts with circuit layout methods used to make PCB's. While there are readily available computer software packages or program suites that can aid designers in either of these fields, these programs are generally incompatible and, so, difficult to use in combination. This incompatibility is fundamental to the design methodologies and is not merely an issue of translating between different data formats.
The software packages for circuit design allow information about the placement of components on the PCB and the required connections among these components to be provided as an input data file, such as a netlist. The subsequent work of laying out the traces and vias is constrained by the obligation to meet topological restrictions imposed by the input data file. Many of these program packages provide automatic trace routing algorithms which do some or all of the job with varying degrees of competence. All packages allow manual routing, in which traces and vias may be moved on the PCB while the circuit connections are preserved. Neither the automatic algorithms nor the ability to move traces and vias is a part of the available methodology of conventional mechanical engineering design packages used to design three-dimensional objects. Conversely, the circuit layout and design packages do not admit of the existence of a third dimension, except in that they may provide for several parallel layers of circuit traces and the local connection between them.
The interrelationship between electrical and mechanical designs is very strong. Even in the design of flat circuit boards, the through-holes which link circuit traces on opposite sides of the board and the holes which are used to support or attach components to the board are recognized as existing on all layers. Furthermore, many of these holes (i.e. vias) are logically associated with the traces.
When a designer adjusts a design in the electrical design package by moving a trace and, so, causing a via to be moved, the computer software attempts to preserve the electrical-mechanical relationship by adjusting the routing on all layers of the board to conform to the new position of the via. Thus, in the electrical packages, a mechanical feature is automatically adapted to circuit requirements. In the mechanical engineering design packages, such topological relationships are not recognized. Mechanical features such as patterns of holes may be moved as a group, but, in general, there is no way of relating these features to the continuity of adaptable decorative details on the surface of the object.
In attempting to extend circuit layout to surfaces in three dimensions, a new set of problems arise due to the limitations of the two-dimensional circuit layout tools. When a solid part is to have circuit traces drawn, for example, on its inner and outer surfaces, electrically identical traces on the two surfaces may be very different due to the thickness of the part near edges or corners, or due to features that break the surface on one side but are not replicated on the other side. Thus, features such as stiffening ribs, standoffs, outer walls and mounting structures may make the topologies of two sides of an object very different.
In the implementation of the design of a molded part, tools are generally used which carry, in mechanical form, the image of what would be the artwork (i.e. traces and connecting pads) in normal two-dimensional circuit processes. In some cases, these tools may be generated using normal circuit board processes, for example, when the part includes flat areas which can be dealt with as simple locally flat boards. However, to obtain full benefit of integrating mechanical and electrical designs, it is desirable to allow the traces to follow shaped surfaces. To do this, the tools which are used to form the part should impose the traces on the part.
However, these tools are themselves solid objects which are fabricated by mechanical means such as machining or casting. Consequently, the traces and vias which constitute the electrical circuit should be specified in whatever system is used to fabricate the tools, be it mechanical drawings interpreted by a skilled machinist or input data files which are used to direct the motion of a numerically controlled machine tool.